JPS6382640A - Adjustment of magnetic resonance imaging apparatus - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention generates a magnetic field resonance phenomenon by applying an RF magnetic field to a subject placed in a static magnetic field, and after the RF magnetic field is released. The present invention relates to a method for adjusting a magnetic resonance imaging apparatus that detects magnetic field resonance signals generated from atomic nuclei of a subject.

(Prior art) Magnetic resonance imaging device (hereinafter referred to as MRI device)
The method applies a -like static magnetic field to a desired part of the subject, and uses a transmitting RF coil to form an RF magnetic field perpendicular to this static magnetic field, producing a magnetic field resonance phenomenon only in a specific slice part from which a tomographic image is obtained. Furthermore, after the RF magnetic field is released, a magnetic field resonance signal (hereinafter referred to as MR multiplied signal) generated from the atomic nucleus is detected by a receiving RF coil. Furthermore, the static magnetic field is applied in the X' axis direction (θ from the X axis.

A composite MR multiplied signal is obtained by applying a linear magnetic field gradient with a linear gradient to the rotated coordinate system (rotated coordinate system), and this signal is subjected to Freeier transformation to rotate the X' axis of the slice part within the X-Y plane. A CT image is formed by obtaining projection information in each direction within the XY plane.

In such an MRI apparatus, a prescan for apparatus adjustment is performed before data collection for forming an MR image of a subject. Device adjustment items include magnetic field lock, automatic tuning, automatic power adjustment, and automatic gain adjustment.

Here, magnetic field lock, automatic tuning, and automatic power adjustment are performed by adjusting the static magnetic field strength, receiving frequency, and transmitting pulse power, respectively, so that the peak value of MR (No. 8) is maximized. Gain adjustment is performed by adjusting the gain of the reception system so as to obtain the optimum reception level.

FIG. 3 is an explanatory diagram of the conventional prescan when performing magnetic field lock, automatic tuning, automatic power adjustment, and automatic gain adjustment. In the figure, ■ to n times each indicate one excitation, and TR is Repetition times for each excitation are shown. As is clear from the figure, the conventional prescan is performed sequentially for each adjustment item, such as magnetic field lock, automatic tuning, automatic power adjustment, automatic gain adjustment, etc. Therefore, the time required for bliscan in automatic adjustment of the above four items is T
7 is Tr = (n x'l', l) X 4 = 4n
TR, and if n = 16 times and TR = 1 sec, then
It is also 64 seconds.

As is well known, the imaging time of an MRI device is inevitably longer than that of other imaging devices such as an X-ray CT device. The time required for scanning should be kept as short as possible.

(Problems to be Solved by the Invention) As described above, the conventional adjustment method for an MRI apparatus has the problem that the briscan time becomes long.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an adjustment method that reduces the time required for pre-scanning for device adjustment.

[Structure of the invention]

(Means for Solving the Problems) The present invention executes multi-slices of a subject by changing the carrier frequency of RF pulses transmitted to the subject, and performs different adjustments for each slice. This allows different types of adjustments to be executed in parallel.

(for production) Carrier frequency ω of the RF pulse (excitation pulse).

It is a known fact that by changing little by little, the slice position of the subject P can be moved in the body axis direction as shown in FIG. 2, for example, and this is called multi-slice. The present invention makes active use of this multi-slice principle, and parallelizes multiple types of adjustment by assigning different types of adjustment items to each slice of the multi-slice, thereby reducing the overall Briscan time in device adjustment. We are trying to shorten the time.

(Example) Hereinafter, the present invention will be specifically explained with reference to Examples.

FIG. 1 is an explanatory diagram of pre-scanning in this embodiment, and shows the case where magnetic field lock, automatic tuning, automatic power adjustment, and automatic gain adjustment are performed. In the same figure, 1
thru n indicate one excitation for each slice in the multi-slice, and 'r and I indicate the repetition time of each excitation. As is clear from the figure, in this example, each slice is excited n times (n is a positive integer) from the first slice to the fourth slice, and magnetic field lock, automatic tuning, automatic power adjustment, and automatic gain adjustment are performed for each slice. are allocated, and each adjustment is performed in parallel. This can be explained chronologically as follows.

That is, the carrier frequency ω of the RF pulse. The first excitation is performed in the order of the first slice, the second slice, the third slice, and the fourth slice by changing the , respectively used for automatic gain adjustment.

After completing the first excitation and data collection in the fourth slice, a second excitation is performed again in the order of the first to fourth slices in the same manner as above, and the data obtained thereby is used for each adjustment described above. It will be done.

Similarly, the third to nth excitations are performed in the order of the first to fourth slices, and the prescan in the tree embodiment ends when the nth excitation and data collection in the fourth slice are completed.

Here, each of the above adjustments is performed based on data obtained by excitation n times for each slice.

That is, magnetic field locking is performed by changing the static magnetic field strength every n excitations in the first slice and automatically adjusting the static magnetic field strength so that the MR multiplied signal peak value is maximized. The capacitance of the tuning capacitor in the receiver circuit is changed every n excitations in two slices, and the tuning capacitor is automatically adjusted so that the peak value of the MR multiplied signal is maximized. This is done by changing the transmission pulse power every n excitations in a slice and automatically adjusting the power supplied to the transmission coil so that the MR multiplied signal peak value is maximized.
The automatic gain adjustment is performed by automatically setting the optimum amplification degree of the amplifier in the reception system based on the reception level every n times of excitation in the fourth slice.

The time T required for the prescan for the above adjustment is approximately nxTR, and if n=16 times and TR=1 sec, then it is 15 sec. This value is 1/4 of the conventional value.

In this way, this embodiment utilizes the principle of multi-slice to parallelize multiple types of adjustment by assigning different types of adjustment items to each slice. Scanning time can be shortened.

Although one embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to the above-described embodiment and includes various modifications.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide an adjustment method that reduces the time required for pre-scanning for device adjustment.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of one embodiment of the present invention, FIG. 2 is an explanatory diagram of multi-slice, and FIG. 3 is an explanatory diagram of a conventional example. (Top and bottom #color)

Claims (1)

[Claims] In a method for adjusting a magnetic resonance imaging apparatus that forms a magnetic resonance image of a subject, multi-slices of the subject are performed by changing the carrier frequency of RF pulses transmitted to the subject, and different adjustments are made for each slice. A method for adjusting a magnetic resonance imaging apparatus, characterized in that a plurality of types of adjustments are executed in parallel by performing the following steps.